U.S. patent number 3,608,868 [Application Number 04/777,367] was granted by the patent office on 1971-09-28 for continually mixing and kneading device with two or more screws for a plasticizable material.
This patent grant is currently assigned to Werner & Pfleiderer. Invention is credited to Heinz Koch.
United States Patent |
3,608,868 |
Koch |
September 28, 1971 |
CONTINUALLY MIXING AND KNEADING DEVICE WITH TWO OR MORE SCREWS FOR
A PLASTICIZABLE MATERIAL
Abstract
A continuously operating device for homogeneously mixing
components of a plasticizable material has an input zone including
unidirectionally rotating meshing screw elements for mixing
components of the material received therein and feeding the mixed
components to a dispersion zone also including rotatable meshing
screw elements. The dispersion zone, in turn, conveys the
components received therein from the input zone, after dispersing
the same, to a mixing zone the screw elements of which have fewer
threads than the screw elements in the dispersion zone and are
preferably not in mesh whereby the components are homogeneously
mixed when leaving the mixing zone. Instead of using one dispersion
zone and one mixing zone two or more such couples may be provided
in one device. Due to the arrangement of the screw elements in the
mixing zone the desired homogeneous mixture is obtained at the
downstream end of the mixing zone.
Inventors: |
Koch; Heinz (Ludwigsburg,
DT) |
Assignee: |
Werner & Pfleiderer
(Stuttgart-Feuerbach, DT)
|
Family
ID: |
25754469 |
Appl.
No.: |
04/777,367 |
Filed: |
November 20, 1968 |
Foreign Application Priority Data
|
|
|
|
|
Dec 16, 1967 [DT] |
|
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P 16 79 884.8 |
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Current U.S.
Class: |
366/82;
366/85 |
Current CPC
Class: |
B29C
48/395 (20190201); B29B 7/483 (20130101); B29B
7/489 (20130101); B29C 48/402 (20190201); B29C
48/03 (20190201) |
Current International
Class: |
B29C
47/40 (20060101); B29C 47/38 (20060101); B29B
7/48 (20060101); B29B 7/34 (20060101); B01f
007/02 (); B29b 001/10 () |
Field of
Search: |
;259/6,104,103,21,41,40 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chi; James Kee
Claims
What is claimed, is:
1. A continually operating device for homogeneously mixing
components of a plasticizable material, said device comprising in
combination:
a casing having a discharge end;
an input zone in said casing including two unidirectionally
rotatable meshing parallel screw elements each having several
threads for mixing components of the material fed into said input
zone and conveying the mixed components toward the discharge end of
the casing;
a dispersion zone disposed in the casing downstream of said input
zone, said dispersion zone including two parallel meshing rotatable
dispersion elements each having several threads for dispersing
components received therein from the input zone and conveying the
resulting mixture toward the discharge end of the casing; and
a mixing zone disposed in the casing downstream of and adjacent to
said dispersion zone, said mixing zone including two coacting
parallel screw elements, said screw elements in the mixing zone
having fewer threads than the dispersion elements in the dispersion
zone whereby flows of material delivered from the dispersion zone
to the mixing zone are combined so as to reduce the number of
delivered flows in the latter zone thus effecting intensive mixing
of the material in the mixing zone.
2. The device according to claim 1 wherein the screw elements in
the mixing zone have fewer threads than the screw elements in the
input zone.
3. The device according to claim 1 wherein the two screw elements
in the input zone and the two dispersion elements in the dispersion
zone respectively are in tight mutual engagement one with the
other.
4. The device according to claim 1 wherein the two dispersion
elements in the mixing zone have diameters such that the elements
are out of mesh but coact in tangential relationship with each
other.
5. The device according to claim 1 wherein the two screw elements
in the mixing zone coact in tangential relationship with each
other, and wherein the turns of said screw elements have a pitch
different one from the other.
6. The device according to claim 4 wherein the cross-sectional
areas of the two screw elements in the mixing zone are smaller than
the corresponding cross-sectional areas of the elements in the
input zone and the dispersion zone.
7. The device according to claim 1 and further comprising a
discharge zone downstream of the discharge end of the mixing zone
in communication therewith, said discharge zone including two
unidirectionally rotatable parallel meshing screw elements having
more threads than the screw elements in the mixing zone.
Description
BACKGROUND
The invention relates to a continuously operating mixing and
kneading device for components of plasticizable material and more
particularly to a mixing and kneading device with two or more
unidirectionally rotating screws in tight mesh with each other at
least in the input zone and the dispersion zone of the device.
Mixing and kneading devices of the general kind above referred to
have excellent dispersion capabilities and also effect a
satisfactory mixing within a narrow spectrum of dwell time within
the device. A disadvantage of such devices is that they have a very
poor mixing capability in lengthwise direction whereby it is not
possible to compensate for dosing inaccuracies when additives are
used. It may be mentioned in this connection that such inaccuracies
are always present as it is virtually impossible in practice to
feed small quantities of additives such as dyestuffs continually
with high dosing accuracy. As it is obvious, the quality of the
material to be processed may suffer very substantially by such
inaccuracies in the dosing.
Various attempts have been made to design the aforereferred to
devices so that they retain the high-grade dispersing capabilities
and also have an acceptable mixing capability in lengthwise
direction.
It has, for instance, been suggested to interpose adjustable
throttling means between the casing of the device and the screws
therein to permit an adjustment of the mixing and kneading action
independent of the rotational speed of the screws.
It has also been proposed to provide spaced apart and staggered
baffle plates on both screw shafts between the conveying elements
thereon to obtain a broader dwell time spectrum.
The mixing action in lengthwise direction can, of course, also be
improved by using deeply cut screws.
However, all the aforelisted structures entail other and very
significant disadvantages. It has been found that the dispersion
capability of the device is adversely affected. When shallower
threads and positively conveying screws are used throttling means
do not produce the desired improvement of the mixing action in
lengthwise direction if, for instance, high polymer materials such
as rubber, are to be processed. Baffle plates delay the rate of
flow through the device and also tend to cause a substantial
increase in the temperature of the mixture to be processed.
THE INVENTION
It is a broad object of the invention to provide a novel and
improved continuously operating mixing and kneading device of the
general kind above referred to which effects a good mixing action
in lengthwise direction without adversely affecting the dispersion
action of the device and without having the afore expalined
disadvantages.
The aforepointed out objects, features and advantages and other
objects, features and advantages which will be pointed out
hereinafter are obtained by providing downstream of a dispersion
zone, which in turn is downstream of an input zone, a mixing zone
including coacting screw elements which have less threads than the
screw elements in the dispersion zone.
It has been found that the components used in the material fed into
the input zone of the device are not thoroughly and homogeneously
mixed in this zone but tend to travel through the input zone and
also through the subsequent dispersion zone in the form of more or
less separate streams. The same applies to additives fed into the
device either at the feed end thereof or at intermediate points.
Due to the provision of fewer threads for the screw elements in the
mixing zone than for the screw elements in the dispersion zone,
such streams of components and additives are broken up and a
thorough homogeneous mixing of all the components and additives
used in the material to be processed is effected. Accordingly, the
material leaving the downstream end of a mixing zone constitutes a
homogeneous mixture of all components and additives which have been
supplied to the device at any point of the length thereof anterior
of the downstream end of the dispersion zone. In other words,
differences in the concentration of the material of the components
and additives contained in and travelling along the individual
screw turns are eliminated thus accomplishing the aforepointed out
broad object of the invention.
Depending upon the composition of the material to be processed the
specific structure of the screw elements in the mixing zone may be
varied.
For certain fields of application the screw elements in the mixing
zone may have a comparatively open profile. In other fields of
application, the diameters of the coacting screw elements in the
mixing zone are such that the screw elements do not mesh but coact
with each other in tangential relationship.
The pitch of the screw elements in the mixing zone may be different
one from the other. The use of a different pitch for the screw
elements is particularly advantageous when nonadhering or so-called
"rolling" materials are to be processed. It is evident that the
differences in pitch of the coacting screw elements in the mixing
zone will result in a marked increase in the action in lengthwise
direction.
It is also possible to obtain the desired lengthwise mixing action
by using smaller cross-sectional areas for the screw elements in
the mixing zone than for the screw elements in the dispersion zone.
Such reduction in cross-sectional areas is particularly
advantageous when the material to be processed is sensitive to
temperature.
Any desired number of mixing zones as previously described may be
provided in one device. For instance, an input zone and a
dispersion zone may be followed by a mixing zone according to the
invention which in turn, is followed by a second dispersion zone
again followed by a mixing zone according to the invention.
To add components or additives to the device in addition to those
initially fed to the device a feed port or other feeding means may
be provided at the upstream end of one or more dispersion
zones.
In the accompanying drawing a preferred embodiment of the invention
is shown by way of illustration and not by way of limitation.
In the drawing:
FIG. 1 shows diagrammatically a fragmentary longitudinal section of
a mixing and kneading device according to the invention;
FIG. 2 is a section taken on either lines 2--2 of FIG. 1;
FIG. 3 is a section taken on line 3--3 of FIG. 1; and
FIG. 4 is a section taken on line 4--4 of FIG. 1.
In FIG. 1 only those structural components of the device which are
essential for the understanding of the invention are shown to
simplify the illustration. The device should be visualized as being
equipped with suitable and conventional power drive means for
rotating the screws of the device, with feed means at the inlet end
and discharge means at the outlet end, intermediate ports for
feeding additives if desired, and ducts in the casing and in the
screw elements to maintain the device at the desired temperature,
etc.
Describing now FIG. 1 more in detail, there is shown a drum or
casing 3 which includes an input zone 1, a dispersion zone 2, a
mixing zone 4 and a discharge zone 5. Accordingly, the material to
be processed moves through the drum from left to right. All zones
include twin screw elements the specific structure of which will be
more fully explained hereinafter.
Input zone 1, that is the zone into which the components of the
material to be mixed are fed comprises two screw elements 6 and 7
which are in tight mesh as clearly shown and are multiple thread
screw unidirectionally rotated. Both screws are shown as having
three threads 6a and 7a respectively of equal pitch. Of course,
more than three threads may be provided. The dispersion zone 2
includes two kneading elements each comprising five mutually
staggered kneading discs 8, 9, 10, 11 and 12 as shown in FIG. 3.
Discs 8 and 12 occupy the same angular relationship so that only
four discs of each kneading element are visible in this figure.
As is evident, multiple thread screw elements instead of discs
could be used in the dispersion zone as kneading elements.
The mixing zone 4 which as previously explained, serves to break up
and mix homogeneously any streams or strings and concentrations of
components or additives which may still exist when the material
enters the mixing zone comprises screw elements 13 and 14. As is
clearly shown, the screw elements 13 and 14 are multiple thread
screw having less threads than the kneading elements in the
dispersion zone, to wit, two threads 13a and 14a respectively as
shown in FIG. 4. As it is evident, the kneading elements in the
dispersion zone 2 will deliver three flows of material to the
mixing zone 4. These three flows will be automatically combined to
two flows in the mixing zone due to the provision of only two
threads in this zone, thereby effecting a forceful and intimate
mixing of the material in this zone. In other words, the concept of
the invention sides in reducing in the mixing zone the number of
flows of material delivered to this zone from the dispersion zone.
The pitch of screw element 13 may be different from that of screw
element 14. To permit coaction of screw elements with a different
pitch and also with a different number of threads the diameters of
screw elements 13 and 14 are reduced so that the screw elements are
not in mesh but coact in tangential relationship. As previously
explained, the structure of the screws in zone 4 causes the desired
homogeneous mixture of all the components and additives, if any,
when and while the material passes through the zone. Accordingly,
the material after it has travelled through the device from the
inlet end thereof to the downstream end of zone 4 is in homogeneous
condition.
Finally, the discharge zone 5 has screw elements 15 and 16 similar
to screw elements 6 and 7, that is, the screw elements are in tight
mesh with each other and have each three threads. Accordingly, FIG.
2 applies to zone 5 also.
While the screw elements are shown in the several figures as
one-piece elements, it is also possible and within the scope of the
invention to provide core shafts on which sleeves with multiple
threads or gangs are fixedly seated.
* * * * *